There are two main sizes of ceiling tile produced on a large scale:600 x 600mm and 1200 x 600mm. However, the actual sizes measure marginally less to fit with the grid: 595 x 595mm and 1195 x 595mm respectively. (Tile sizes vary across manufacturers but most are 595 square). The larger sizes refer to the nominal ‘centre to centre’ sizes of the grid for setting out. The 5mm difference allows for a bit of tolerance to position the tile in the grid whilst fitting.